Servo-control apparatus for motor

ABSTRACT

The present invention provides a servo-control apparatus for a motor, comprising position detecting means for detecting a rotational position of a motor, rotational speed signal generating means for generating a rotational speed signal corresponding to a rotational speed of a motor, and digital control means for generating an exciting electric current to be supplied to a coil of the motor as a PWM signal in accordance with the rotational speed signal from the rotational speed signal generating means, and wherein a switching signal for switching the exciting electric current to be supplied to the coil of the motor is formed by a pre-driver in accordance with the position detection signal from the position detecting means, and the pre-driver combines the switching signal with the PWM signal from the digital control means to generate an electric current control signal by which the motor is driven, thereby coping with the speed change of the motor quickly and stably.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a servo-control apparatus for motor, servo-controlling a motor by using a DSP as digital control means, and more particularly it relates to a motor servo-control apparatus suitable for controlling a plurality of motors used in an image forming apparatus.

[0003] 2. Related Background Art

[0004]FIGS. 12 and 13 are conventional circuit diagrams for effecting servo-control of a plurality of motors by using a micro computer. Particularly, FIG. 12 is a block diagram showing an entire circuit in which a plurality of motor units 301 having the same construction are connected to a single micro computer 300, and FIG. 13 is a block diagram showing an internal construction of one of the motor units 301.

[0005] Now, the conventional servo-control will be described. In FIGS. 12 and 13, there are shown a micro computer 300, motor units 301, a control IC 302, a three-phase motor 303, three hole sensors 304 for detecting a position of a main pole of a rotor, an FG sensor 305 for detecting a pattern magnetized on the rotor and for outputting 36 pulses per one revolution of the motor, an oscillator 306, a current detecting resistor 307, a control portion 308, a driver portion 309, an electric current limiter detecting portion 310, a speed control portion 311, a frequency divider 312, an integration amplifier 313, resistors and capacitors constituting integration filters 314 to 317, a control signal 318 emitted from the micro computer 300 and adapted to drive/stop the motor, and a ready signal 319 which becomes active when the motor reaches a predetermined revolution number.

[0006] Next, an operation of the circuit will be described. When a motor driving command is emitted from the micro computer 300 controlling an image forming apparatus through the signal line 318, the control portion 308 detects the position of the main pole of the rotor of the motor 303 by the hole sensors 304 and forms a three-phase exciting pattern so as to rotate the motor in a desired direction and sends an exciting signal to the driver portion 309. On the basis of the exciting signal, the driver portion 309 drives an output transistor (not shown) so that an electric current direction with respect to a coil of the motor is switched to generate desired excitation. On the other hand, when the rotor of the motor 303 is rotated, predetermined pulses are generated by the FG sensor 305 and are sent to the speed control portion 311. In the speed control portion 311, a reference clock formed by the oscillator 306 and the frequency divider 312 is compared with the pulse detected by the FG sensor 305, and the difference therebetween is outputted.

[0007] Incidentally, the reference clock is set to obtain a target revolution number (number of revolutions) of the motor. Namely, when the FG sensor outputs 30 pulses per one revolution of the motor, in order to rotate the motor at 600 rpm, the reference clock of 300 Hz (=(600/60)×30) may be given.

[0008] The difference with respect to the target speed obtained by the speed control portion 311 is integrated by the integration amplifier 313, and a result is sent to the driver portion 309. In this case, gain and a phase compensation value are determined by the resistors and capacitors 314 to 317. These constants are referred to as servo constants.

[0009] Further, in the drover portion 309 for the motor of the conventional image forming apparatus, a transistor of bipolar type is used. Thus, since heat loss of the driver portion is great, a radiator plate is provided. Further, in order to reduce heat generation due to such heat loss as much as possible, efficiency of the motor must be increased so that a desired power be obtained with least electric power. To this end, a brushless motor of outer rotor type having good efficiency is used.

[0010] As mentioned above, in the conventional circuit arrangement, the motor is controlled by sending only stop/start signals to the motor units 301 from the micro computer 300, and a servo-control loop is formed in each motor unit 301. The reason is that, the processing ability of the conventional micro computer has limitation, servo-control must be effected in each motor unit 301. As the processing ability of the micro computer or a DSP (digital signal processor) has been improved, the servo-control for the motors has been able to be effected by the micro computer or the DSP itself. Further, due to increase in processing ability of the DSP, a plurality of motors have been able to be servo-controlled independently.

[0011] As a result, in place of the above-mentioned conventional circuit arrangement, it is considered to provide a circuit in which motors are servo-controlled by using the DSP. Such a circuit normally considered will be explained hereinbelow. FIGS. 14 and 15 are views showing such a circuit normally considered. Particularly, FIG. 14 is a block diagram showing an entire circuit in which a plurality of motor units are connected to a single DSP, and FIG. 15 is a block diagram showing an internal construction of one of the motor units.

[0012] In FIGS. 14 and 15, there are shown a DSP 501 serving to control six motors 505, motor units 502 each including a drive circuit, a driver 504, a three-phase DC brushless motor 505, a charge pump circuit 401 for generating gate voltage for N-chMOS of the driver 504, pre-driver circuits 402 to 407, exciting switching signals 408 to 413, a current sense signal 414, hole sensor signals 415 to 417, an MR sensor signal 418, hole sensor amplifiers 419 to 421, an MR sensor amplifier 422, N-chMOS transistors (driver portions) 515 to 520, a current detecting resistor 521, U-phase output 522 connected to a U-phase coil of the motor, V-phase output 523 connected to a V-shape coil, W-phase output 524 connected to a W-phase coil, hole sensors 525 to 527, an MR sensor 528, and a serial communication bus 532 for effecting communication with a control CPU (not shown) of the image forming apparatus.

[0013] Next, an operation of this servo-control circuit will be described. First of all, when motor drive command is emitted from the CPU through the serial communication line 532, the DSP 501 ascertains the position of the rotor detected by the hole sensors 525 to 527 on the basis of the hole sensor signals 415 to 417 and determines the switching timing so as to obtain the desired rotation and effects control on the basis of the switching signals 408 to 413 to give desired rotational direction and desired electric current to the motor.

[0014] Namely, the N-chMOS transistors 515 to 520 are switched to give the desired rotational direction, and the N-chMOS transistors 515, 517, 519 are PWM-switched to flow the desired electric current into the coil of the motor. In this case, the gate voltages of the N-chMOS transistors 515, 517, 519 are increased to Vcc+10V by the charge pump circuit 401.

[0015] For example, when the DSP 501 ascertains the rotor position of the motor on the basis of the hole sensor signals 415 to 417 amplified by the hole sensor amplifiers 419 to 421 and the hole sensors 525 to 527 and switches the direction of the electric current from the U-phase 522 to the W-phase 523 to obtain the desired rotational direction, the pre-drivers 402 to 407 turn ON the N-chMOS transistors 515, 518 and turn OFF the transistors 516, 517, 519, 520. As a result, an electric current path extends from Vcc to the current detecting resistor 521 through the transistor 515, U-phase output 522, V-phase output 523 and transistor 518, thereby generating a magnetic force in the desired coil. In this case, the PWM signal given by the DSP 501 is composed or combined with the switching signal 408, so that the N-chMOS transistor 515 is PWM-controlled by the pre-driver 402.

[0016] Accordingly, ON-duty electric current defined by the PWM signal flows from the U-phase to the V-phase. In this way, the motor is subjected to exciting switching control for switching the electric current to U, V, W-phase to rotate the rotor in the desired rotational direction, thereby generating torque by relative electromagnetic action between the main pole magnet (not shown) and the coil.

[0017] When the motor is subjected to the exciting switching control in this way to rotate the rotor, a pre-set MR sensor magnetizing pattern is detected by the MR sensor 528, thereby outputting 360 pulses per one revolution. Namely, a signal having frequency corresponding to the revolution number of the motor is obtained, and this signal is inputted to the DSP 501 as the MR sensor signal 418 through the amplifier 422.

[0018] The DSP 501 measures a pulse interval of the MR sensor signal 418 and seeks the speed (rad/s) of the motor and compares the motor speed with a target control speed and performs PI filter (not shown) and gain added calculation (not shown) to derive PWM pulse width and combines the pulse width with the switching signals 408, 410, 412 to control the current to be supplied to the motor coil, thereby controlling the motor to rotate at the target speed.

[0019] In this way, the DSP 501 effects the switching of the output stage N-chMOS transistor by generating the PWM signal and combining it with the switching signals, thereby performing the servo-control to rotate the motor at the desired number of revolutions. On the other hand, the position of the main pole is detected by the hole sensors 525 to 527, and the switching control is performed on the basis of the hole sensor signals 415 to 417 to rotate the rotor in the desired rotational direction. Further, the current flowing through the motor is detected by the electric current detecting resistor 521, and, there is provided protecting means for limiting the electric current if the current greater than a predetermined value flows.

[0020] In the conventional motor servo-control apparatus explained in connection with FIGS. 12 and 13, the micro computer effects drive/stop control of the drive motors, and each drive motor has serve-control IC and the serve-control is effected in each motor unit. Namely, the feedback loop is closed in the motor unit. Further, stability of the servo-control of each motor is determined by constants, i.e., serve constants of the resistors and capacitors connected to the integration amplifier of the circuit. Namely, these servo constants were required to be set so that the motors be rotated most stably and accurately under every conditions in consideration of load inertia and load torque.

[0021] As a result, when the above-mentioned conventional motor servo-control apparatuses are used as various drive means of an image forming apparatus of electrophotographic type having a cartridge integrally including toner and a photosensitive drum, if load inertia and torque of the drive motor for driving the photosensitive drum is greatly changed in dependence upon difference in toner capacity, difference in kind of toner or difference in cartridge, there arose a problem that stable servo-control could not achieved under every conditions.

[0022] Further, in a color image forming apparatus, in order to enhance a glossy property, there is provided a glossy print mode in which a recording paper is conveyed at a speed slower than a normal recording paper conveying speed so that a time period during which the recording paper is passed through a fixing device is increased to improve toner fusion. Thus, the drive motors must be controlled with plural speeds, and, if the speed control range is wide, stable servo-control cannot be obtained by only one servo constant system.

[0023] As one method for solving this problem, there has been proposed a technique in which a plurality of integration amplifiers are provided and the amplifiers are switched in accordance with the condition. However, this technique has a disadvantage that the cost is increased considerably.

[0024] Further, in general, speed detecting means for the servo motor is provided on the motor itself, for the purpose of improvement in rotational accuracy and stability of the rotor of the motor.

[0025] In an image forming apparatus using such a motor, for example, if fluctuation in rotation due to fluctuation in load is caused on a shaft of a photosensitive drum, when such fluctuation in rotation can be corrected by the servo-control of the motor, the fluctuation in rotation of the drum shaft can be reduced, thereby obtaining good image quality. However, since the conventional motor is a DC bruchless motor of outer rotor type having a main pole magnet of the rotating rotor, inertia of the rotor is great. Accordingly, the fluctuation in rotation generated on the drum shaft is hard to be transmitted to a drive shaft of the drum drive motor. As a result, even if the servo-control of the drum drive motor is performed accurately, unevenness in rotation of the drum cannot be improved, with the result that deterioration of image quality cannot be reduced.

[0026] Further, there is an image forming apparatus using a stepping motor in place of the DC brushless motor. However, the stepping motor has low efficiency in comparison with the DC brushless motor. Thus, particularly in the color image forming apparatus having a plurality of motor, if all of the motors are stepping motors, load on the power supply of the apparatus becomes great thereby to increase the total cost of the apparatus considerably. Further, since the stepping motor generates great vibration during step driving, when the plurality of stepping motors are used, noise of the apparatus becomes great.

[0027] As an apparatus normally considered to eliminate the above-mentioned disadvantages of the conventional motor servo-control device shown in FIGS. 12 and 13, there is the motor servo-control apparatus explained in connection with FIGS. 14 and 15. In this servo-control apparatus, since the DSP performs all of the phase switching control, speed control and electric current limiting control, if the number of the motor units connected to the DSP is increased, adequate processing cannot be achieved. Further, since the great number of signal lines are required between the DSP and the motor units (for example, eleven signal lines for each motor unit), the number of input/output pins is increased, with the result that control ability of interfaces may be worsened. Further, in the electric current limitation, when the electric current detection voltage is sent from the motor unit to the DSP, if a distance between the motor unit and the DSP is long, noise will be generated.

[0028] When digital servo-control of the plural motors is effected by the DSP, if control timings for motors are overlapped as the umber of motors to be controlled, since servo-control period of the motor does not become constant, unevenness in rotation of motor will occur.

[0029] Further, the servo constant of the motor to be servo-controlled is determined by torque constant, inertia and coil resistance of the motor to be connected.

[0030] In such a construction, particularly when motors were purchased from plural companies, the servo constant must be set so that stable servo-control can be achieved under all conditions of torque constants, inertia and coil resistances of the motors to be used.

[0031] For example, inertia of the motor of outer rotor type differs greatly from inertia of the motor of inner rotor type. In such motors having different inertia, the setting of proper servo constant has limitation.

[0032] Namely, if the servo constant is set to match with the motor of outer rotor type to enhance the servo stability of the motor of outer rotor type, when the motor of inner rotor type is used, servo stability of such a motor will be worsened.

[0033] Thus, in the past, when the servo constant was selected, it was difficult to enhance the stability of servo-control regarding all of the motors to be used.

SUMMARY OF THE INVENTION

[0034] The present invention aims to eliminate the above-mentioned conventional drawbacks and an object of the present invention is to provide a motor servo-control apparatus which has a construction suitable for effecting servo-control by using a DSP as digital control means.

[0035] Another object of the present invention is to provide a motor servo-control apparatus in which a plurality of motors used in an image forming apparatus are controlled collectively by using a DSP as digital control means.

[0036] The other objects and features of the present invention will be apparent from the following detailed explanation referring to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0037]FIG. 1 is a schematic view showing an image forming apparatus according to the present invention;

[0038]FIG. 2 is a view showing a motor servo-control apparatus used in the image forming apparatus of FIG. 1 and particularly showing a block diagram of an entire circuit in which a plurality of circuit units are connected to a single DSP;

[0039]FIG. 3 is a block circuit diagram showing internal circuitry of one of the plural motor units shown in FIG. 2;

[0040]FIG. 4 is a block diagram showing the DSP of FIGS. 1 and 2 concretely;

[0041]FIG. 5 is a view showing control of the plural motors of FIG. 4 in a time-lapse relation;

[0042]FIG. 6 which comprised of FIGS. 6A and 6B is a flow chart showing motor control program of DSP including servo constant calculation control;

[0043]FIG. 7A is a view showing a brushless motor o f outer rotor type as a reference, and FIG. 7B is a view showing a brushless motor of inner rotor type used in the present invention;

[0044]FIG. 8 is a block circuit diagram showing a first alteration of the internal circuitry of the motor unit shown in FIG. 3;

[0045]FIG. 9 is a flow chart of DSP shown in FIG. 8;

[0046]FIG. 10 is a block circuit diagram showing a second alteration of the internal circuitry of the motor unit shown in FIG. 3;

[0047]FIG. 11 is a flow chart of DSP shown in Fg 10;

[0048]FIG. 12 is a block diagram of an entire circuit showing a conventional motor servo-control apparatus in which a plurality of motor units are connected to a single micro computer;

[0049]FIG. 13 is a block circuit diagram showing internal circuitry of one of the plural motor units shown in FIG. 12;

[0050]FIG. 14 is a block diagram of an entire circuit in which a plurality of motor units are connected to a single DSP, which can be considered in connection with the conventional motor servo-control apparatus; and

[0051]FIG. 15 is a block circuit diagram showing internal circuitry of one of the plural motor units shown in FIG. 14.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0052] The present invention will now be explained with reference to the accompanying drawings.

[0053] Prior to explanation of a motor servo-control apparatus of the present invention, first of all, an image forming apparatus to which the motor servo-control apparatus of the present invention can be applied will be described.

[0054]FIG. 1 is a schematic view showing such an image forming apparatus. In FIG. 1, the image forming apparatus 201 comprises a sheet cassette 202, a pick-up roller 203, an electrostatic belt drive roller 204, an electrostatic belt 205, an yellow photosensitive drum 206, a magenta photosensitive drum 207, a cyan photosensitive drum 208, a black photosensitive drum 209, an yellow transfer roller 210, a magenta transfer roller 211, a cyan transfer roller 212, a black transfer roller 213, an yellow cartridge 214, a magenta cartridge 215, a cyan cartridge 216, a black cartridge 217, an yellow optical unit 218, a magenta optical unit 219, a cyan optical unit 220, a black optical unit 221, a fixing roller 222 and a sheet path 223.

[0055] The image forming apparatus serves to perform an electrophotographic process on the basis of command from a host computer (not shown) to transfer yellow, magenta, cyan and black images onto a paper in a superimposed fashion. Further, the pick-up roller 203 is driven by a pick-up roller motor, the electrostatic belt is driven by a belt motor, the photosensitive drums are driven by respective color drum motors, and the fixing roller is driven by a fixing motor, and drive/stop of each motor is controlled by a servo-control apparatus provided in the image forming apparatus.

[0056]FIGS. 2 and 3 are views showing the motor servo-control apparatus according to the present invention. Particularly, FIG. 2 is a block diagram showing an entire circuit in which six motor units of the image forming apparatus are connected to a single DSP, and FIG. 3 is a block diagram showing an internal construction of one of the motor units (motor unit 502 having an yellow photosensitive drum motor 505 ₁.

[0057]FIGS. 2 and 3, a DSP (digital signal processor) 501 as a digital control device is capable of performing product/addition calculation quickly. Motor units 502 includes drive circuits (pre-driver, driver) and have the same construction and comprise, from the above, a motor unit having an yellow photosensitive drum motor 505 ₁, a motor unit having a magenta photosensitive drum motor 505 ₂, a motor unit having a cyan photosensitive drum motor 505 ₃, a motor unit having a black photosensitive drum motor 505 ₄, a motor unit having a belt motor 505 ₅, and a motor unit having a fixing motor 505 ₆. Incidentally, the pick-up roller 203 is driven by a stepping motor which does not relate to the servo-control apparatus of the present invention. The DSP 501 serves to control six motors 505 ₁ to 505 ₆. As each of these motors, a DC brushless motor of inner rotor type having small inertia and capable of improving control accuracy is used. In FIG. 3, there are shown a pre-driver 503 having a logic circuit and a control circuit which will be described later, a driver 504, a three-phase DC brushless motor 505, a regulator 506, a charge pump circuit 507 for generating gate voltage for N-chMOS of the driver 504, a logic circuit 508 for composing or combining a PWM signal from the DSP 501 with switching signals (which will be described later), a control circuit 509 for boosting output from the logic circuit, an electric current limiter 510, hole sensor amplifiers 511 to 513, an MR sensor amplifier 514, N-chMOS transistors 515 to 520 provided in the driver, an electric current detecting resistor 521, a U-phase output 522 connected to a U-phase coil of the motor, a V-phase output 523 connected to a V-phase coil, a W-phase output 524 connected to a W-phase coil, hole sensors 525 to 527, an MR sensor 528, a motor start signal (stop/start signal) 529 outputted from the DSP, a PWM signal 530 outputted from the DSP, and a motor speed detecting MR sensor signal 531. The logic circuit serves to combine the switching signals from the hole sensors 525 to 527 through the hole sensor amplifiers 511 to 513 with the PWM signal from the DSP 501, and the control circuit 509 serves to boost an output signal from the logic circuit 508 to be outputted to the driver 504 as an electric current control signal. There is also provided a serial communication bus 532 for effecting communication with a control CPU (not shown) of the image forming apparatus.

[0058] Next, an operation of the motor servo-control circuit will be described. First of all, when a motor drive command is emitted from the CPU through the serial communication line 532, the pre-driver 503 ascertains the position of the rotor detected by the hole sensors 525 to 527 and determines the switching timing so as to obtain the desired rotation and effects control give desired rotational direction and desired electric current to the motor. Namely, the N-chMOS transistors 515 to 520 are switched to give the desired rotational direction, and the N-chMOS transistors 515, 517, 519 are PWM-switched to flow the desired electric current into the coil of the motor. In this case, the gate voltages of the N-chMOS transistors 515, 517, 519 are increased to Vcc+10V by the charge pump circuit 507.

[0059] For example, when the pre-driver 503 ascertains the rotor position of the motor on the basis of the hole sensor signals amplified by the hole sensor amplifiers 511 to 513 and the hole sensors 525 to 527 and switches the direction of the electric current from the U-phase 522 to the W-phase 523 to obtain the desired rotational direction, the pre-driver 503 turns ON the N-chMOS transistors 515, 518 and turns OFF the transistors 516, 517, 519, 520. As a result, an electric current path extends from Vcc to the current detecting resistor 521 through the transistor 515, U-phase output 522, V-phase output 523 and transistor 518, thereby generating a magnetic force in the desired coil. In this case, the PWM signal 530 given by the DSP 501 is composed or combined with the switching signal, so that the N-chMOS transistor 515 is PWM-controlled b the pre-driver 503.

[0060] Accordingly, ON-duty electric current defined by the PWM signal flows from the U-phase to the V-phase. In this way, the motor is subjected to exciting switching control for switching the electric current to U, V, W-phase to rotate the rotor in the desired rotational direction, thereby generating torque by relative electromagnetic action between the main pole magnet (not shown) and the coil.

[0061] When the motor is subjected to the exciting switching control in this way to rotate the rotor, a pre-set MR sensor magnetizing pattern is detected by the MR sensor 528, thereby outputting 360 pulses per one revolution. Namely, a signal having frequency corresponding to the revolution number of the motor is obtained, and this signal is inputted to the DSP 501 as the MR sensor signal 531 through the amplifier 514.

[0062] The DSP 501 measures a pulse interval of the MR sensor signal 531 and seeks the speed (rad/s) of the motor and compares the motor speed with a target control speed (set target speed which can be altered) and performs PI filter (not shown) and gain added calculation (not shown) to derive PWM pulse width and sends the pulse width to the pre-driver 503 as the PWM signal 530 to control the current to be supplied to the motor coil, thereby controlling the motor to rotate at the target speed.

[0063] In this way, the DSP 501 effects the switching of the output stage N-chMOS transistor by generating the PWM signal and combining it with the switching signals, thereby performing the servo-control to rotate the motor at the desired number of revolutions. On the other hand, the position of the main pole is detected by the hole sensors 525 to 527, and the switching control is performed by the pre-driver 503 on the basis of the hole sensor signals 415 to 417 to rotate the rotor in the desired rotational direction. Further, the pre-driver 503 detects the current flowing through the motor by the electric current detecting resistor 521, and, there is provided protecting means for limiting the electric current if the current greater than a predetermined value flows.

[0064]FIG. 4 shows an internal construction of the DSP 501 concretely. The reference numeral 529 denotes six motor start signals outputted to the respective motor units; 530 denotes six PWM signals outputted to the respective motor units; and 531 denotes six motor speed detecting MR sensor signals inputted from the respective motor units.

[0065] In FIG. 4, there are shown target speeds 101, 102 for respective motors, in which independent target speeds (rad/s) are set with respect to six motors 505 ₁ to 505 ₆; a target speed selecting portion 103 in the servo-control loop; a calculation point 104 for deriving a difference between the target speeds and actual speeds; PI filter and PWM selecting portion 105 in the servo-control loop; a PI filter 106 for the motor 505 ₁ including PI filter integration item constant 107 for the motor 5051 and a memory portion 108 (of the PI filter for the motor 505 ₁) for storing a preceding calculation result and a proportion item constant 109 of the PI filter for the motor 5051; a PWM pulse width calculation portion 110 for the motor 505 ₁; and a PWM pulse generating portion 111 for the motor 505 ₁. An output from the PWM pulse generating portion 111 is the PWM pulse signal 530 for the motor 505 ₁.

[0066] There are further shown a PI filter 113 for the motor 505 ₆ including PI filter integration item constant 114 for the motor 505 ₆ and a memory portion 115 (of the PI filter for the motor 505 ₆) for storing a preceding calculation result and a proportion item constant 116 of the PI filter for the motor 505 ₆; a PWM pulse width calculation portion 117 for the motor 505 ₆; and a PWM pulse generating portion 118 for the motor 505 ₆. An output from the PWM pulse generating portion 111 is the PWM pulse signal 530 for the motor 505 ₆.

[0067] In this way, the PI filter, PWM pulse width calculation portion, PWM pulse generating portion and PWM signal are provided for each of the motors 505 ₁ to 505 ₆.

[0068] Further, as the motor speed detecting MR sensor signal 531, 360 pulses per one revolution of the motor are inputted. A capture 121 serves to count the pulse obtained by the motor 505 ₁ from edge to edge by a predetermined timer, and a capture 123 serves to count the pulse obtained by the motor 505 ₆ from edge to edge by a predetermined timer. In this way, the pulse signals are given from the respective motors 505 ₁ to 505 ₆, and the capture is provided for each of the motors. The reference numeral 124 denotes a capture selecting portion; 125 denotes a speed calculating portion; and 126 denotes a selector. A CPU communication block 128 serves to output motor start signals 529, and a serial communication bus 532 serves to effect communication with a control CPU (now shown) of the image forming apparatus.

[0069] Next, an operation will be explained.

[0070] First of all, the program of the DSP controls the control loop to cause the selector 126 to select a motor to be controlled so that the controls are not interfered. For example, when six motors are controlled with the same control loop of 1 kHz, if all of the motors ar controlled at the same timing, interference will occur. To avoid this, the phases of the control loops of 1 kHz are deviated from each other.

[0071] When the control of the motor 505 ₁ is selected by the selector 126, a target speed 101 of the motor 505 ₁ is selected, and the selected speed is compared with the speed of the motor 505 ₁ at the calculation point 104. The speed of the motor 505 ₁ to be compared is sought by inputting the pulses (360 pulses per one revolution) generated by the rotation of the motor 505 ₁ is inputted to the capture 121 through the pulse signal line 120 and by selecting it in the capture selecting portion 124 and by calculating the speed in the speed calculation portion 125.

[0072] A compared result obtained at the calculation point 104 is inputted to the PWM selecting portion 105, where the PI filter 106 for motor 1 is selected and PI calculation is effected. The PI calculation is effected by adding a result obtained by multiplying the speed difference (sought at the calculation pint 104) by the proportion item constant 109 to a result obtained by adding the preceding calculation result (stored in the memory portion 108) to a result obtained by multiplying the speed difference by the integration item 107. The proportion constant 109 and the integration constant 107 (which constitute PI filter constant) are referred to as servo constant and are previously set on the basis of the specification of the motor, and load inertia and torque condition of the motor.

[0073] A calculated result in the PI filter 106 is converted into a PWM pulse width in the PWM pulse width calculating portion 110, and the PWM pulse is generated in the PWM pulse generating portion 111. In the PWM pulse generating portion, the PWM pulse having the width sought in the PWM pulse calculating portion 111 is overlapped with pre-set PWM carrier frequency.

[0074] For example, when it is defined that the pre-set PWM carrier frequency is 20 kHz (50 μs) and the PWM pulse width is 8 bits, if the PWM pulse calculation result is “66”H, the PWM pulse width will be 20 μs (=50μs×“66”H/“FF”H), with the result that the PWM pulse signal 530 of 40% (regarding carrier frequency of 20 kHz) is outputted. The pulse width is renewed whenever the calculated result is obtained in the PWM pulse calculating portion 110. Namely, if the PWM calculation is effected with period of 1 kHz, the PWM pulse width will be changed every 1 kHz period.

[0075] As mentioned above, similar to the generation of the PWM pulse for the motor 505 ₁, regarding each of the motors 505 ₂ to 505 ₆, a PWM pulse is generated on the basis of corresponding PI filter constant and PWM carrier frequency. The PI filter constant and PWM carrier frequency are previously set in accordance with the specification of the motor and driving load condition.

[0076] On the other hand, the speed of each of the motors 505 ₁ to 505 ₆ selected by the selector 126 is calculated by selecting the corresponding capture in the capture selecting portion 124 and by reading-in the value of the selected capture and by effecting calculation in the speed calculating portion 125.

[0077] For example, in a case where the capture 121 is 16 bits and clock is 50 ns and pulse signal 120 outputted by the motor 505 ₁ has 360 pulses per one revolution, regarding the speed of the motor 505 ₁, when the value of the capture 121 is “1234”H, the interval between the pulse signal 120 becomes 233 μs (=“1234”H×50 ns) and the speed of the motor 505 ₁ becomes 74.9 rad/s (=(2π/360)/233 μs).

[0078] Next, an operation of the selector 126 will be explained with reference to FIG. 5. FIG. 5 is a view showing the control of the motors 505 ₁ to 505 ₆ in a time-lapse relation. Blocks 801 to 806 indicate control periods of the motors 505 ₁ to 505 ₆, a block 807 indicates a control period of the motor 505 ₁, a block 808 indicates the reading of capture in the control of the motor 505 ₁, a block 809 indicates calculation of speed, a block 810 indicates the setting of target speed, a block 811 indicates calculation of difference between speeds, a block 812 indicates calculation of PI, a block 813 indicates calculation of PWM, a block 814 indicates the outputting of PWM, and the reference numeral 815 indicates a servo-control period of the motor 505 ₁.

[0079] Also regarding the motors 505 ₂ to 505 ₆, the control similar to the blocks 808 to 814 is performed. The servo-control period 815 of the motor 505 ₁ is determined by a response property of the motor 505 ₁. Similarly, the motors 505 ₂ to 505 ₆ are controlled with optimum servo-control periods in consideration of response properties of the motors. In this case, the servo-control periods are controlled by the selector so that the servo-control periods do not interfere with each other.

[0080] For example, when the servo-control periods of the motors 505 ₁ to 505 ₆ are all 1 kHz (1 ms), the control start timing of the motor 505 ₁ is deviated from the control start timing of the motor 505 ₂ by about 166 μs (=1 ms/6). Similarly, deviation between the control start timing of the motor 505 ₂ and the control start timing of the motor 505 ₃, deviation between the control start timing of the motor 505 ₃ and the control start timing of the motor 505 ₄, deviation between the control start timing of the motor 505 ₄ and the control start timing of the motor 505 ₅, deviation between the control start timing of the motor 505 ₅ and the control start timing of the motor 505 ₆ are selected to about 166 μs.

[0081] On the basis of the servo-control period determined for each motor control, the capture of the motor to be controlled is read, the speed is calculated, the target speed of the motor to be controlled is set, the difference between the target speed and the actual speed is calculated, a calculated result is subjected to PI calculation with the PI filter constant for the motor to be controlled, PWM calculation is effected, and the PWM is outputted. Namely, servo-control loops for the respective motors are formed so that they do not interfere with each other, and, the target speeds and PI filter constants (servo constants) inherent to the respective motors are selected, and the respective PWM pulse controls are effected.

[0082] Next, the motor control operation will be explained.

[0083] First of all, for example, when the fixing motor driving command is emitted from the CPU through the serial communication bus 532, the DSP 501 causes the pre-driver 503 to make the motor start signal 529 active and causes the PWM signal 530 to generate PWM pulse having ON-duty of 80%, thereby driving the motor.

[0084] When the motor start signal 529 is received, the pre-driver 503 effects the exciting switching control of the N-chMOS transistors 515 to 520 (in the logic circuit 508) on the basis of the position of the rotor detected by the hole sensors 525 to 527 so that the motor is rotated in the predetermined rotational direction, and, when the PWM signal 530 is received, the pre-driver PWM-switches the N-chMOS transistors 515, 517, 519. In this case, the control circuit 509 increases the gate voltages for the N-chMOS transistors 515, 517, 519 to Vcc+10V through the charge pump circuit 507.

[0085] For example, when the logic circuit 508 ascertains the position of the rotor of the motor on the basis of the result amplified by the hole sensor amplifiers 511 to 513 and the hole sensors 525 to 527 to switch the electric current direction from the U-phase 522 to the V-phase 523 thereby to obtain the desired rotational direction, the N-chMOS transistors 515, 518 are turned On and the N-chMOS transistors 516, 517, 519, 520 are turned OFF. As a result, the electric current path extends from Vcc to the electric current detecting resistor 521 through the N-chMOS transistor 515, U-phase output 522, W-phase output 523 and N-chMOS transistor 518, thereby generating a magnetic force in the predetermined coil.

[0086] In this case, the N-chMOS transistor 515 is PWM-controlled by the PWM signal 530 given by the DSP 501 and passing through the logic circuit 508 and control circuit 509. Accordingly, the ON-duty electric current defined by the PWM signal 530 flows from the U-phase to the V-shape. In this way, the exciting switching control for switching the electric current to the U-phase and V-phase is effected so that the motor is rotated in the predetermined direction, thereby generating torque by relative electromagnetic action between the main pole magnet (not shown) and the coil.

[0087] When the motor is subjected to the exciting switching control to rotate the rotor in this way, the pre-set MR sensor magnetized pattern is detected by the MR sensor 528, and 360 pulses per one revolution are outputted. Namely, the signal having frequency corresponding to the revolution number of the motor is obtained, and this signal is sent to the DSP 501 through the amplifier 514 and the MR sensor signal line 531.

[0088] The program of the DSP 501 measures the pulse interval between the pulses from the MR sensor signal line 531 and seeks the speed (rad/s) of the motor and compares the motor speed with the target control speed and performs PI filter calculation (not shown) and gain addition calculation (not shown) to derive the PWM pulse width and sends the pulse width to the pre-driver through the PWM signal line 530 to control the current to be supplied to the motor, thereby controlling the motor to rotate at the target speed.

[0089] In this way, the DSP 501 effects the switching of the output stage N-chmos transistor by using the PWM signal 530, thereby performing the servo-control to rotate the motor at the desired number of revolutions. On the other hand, the pre-driver 503 performs the exciting control on the basis of the position of the main pole detected by the hole sensors 525 to 527 to rotate the rotor in the desired rotational direction and drives the N-chMOS transistor. Further, the pre-driver detects the current flowing through the motor by the electric current detecting resistor 521, and, there is provided protecting means for limiting the electric current by the current limiter circuit 510 if the current greater than a predetermined value flows.

[0090] As mentioned above, according to the illustrated embodiment, in order that the six motors of the image forming apparatus is subjected to the software servo-control by the single DSP so as to control the motors by using the servo constants pre-set in accordance with various conditions regarding the control revolution number, inertia, torque constant, coil specification and driving load of each motor without interfering the independent servo-control loops of the motors with each other, there is provided the selector means by which the timings of servo-control loops of the motors are governed, and the control loop of each motor regarding the target speed, speed detection, PI filter calculation, PWM calculation and PWM pulse output is controlled.

[0091] As a result, particularly in an image forming apparatus which has a plurality of servo motors and in which a driving load condition is changed within a wide range, stable servo-control can always be realized, thereby obtaining good image quality.

[0092] Further, since the servo-control can be performed efficiently under concentrate control of single DSP, the cost of the image forming apparatus can be reduced.

[0093]FIG. 6 is a flow chart of the motor control program of the DSP including servo constant calculation control, regarding only the motor 505 ₁.

[0094] First of all, in a step S601, it is judged whether there is command for determining the servo constant of the motor 505 ₁ from the control CPU (not shown) of the image forming apparatus. The CPU of the image forming apparatus sends such command to the DSP in a time period in which the motor driving is not required, other than the image forming period.

[0095] I(n the step S601, if there is the servo constant setting command, in a step S602, a servo constant setting control flag is set, and, in a step S603, a timer is set. Then, in a step S604, PWM ON-duty is set to 100%, and, in a step S605, the motor driving signal is made active. Then, in a step S606, it is judged whether the motor speed reaches 63%.

[0096] In the step S606, if the motor speed does not each 63%, the program is jumped and the speed detection and PWM output control are effected. As a result, the motor starts to rotate with an open loop. On the other hand, in the step S606, if the motor speed reaches 63%, in a step S607, the motor is stopped and the PWM ON-duty is made 0%, and, in a step S608, the time is measured on the basis of the previously driven timer. Namely, after the motor is driven with the open loop, a time period until the motor speed reaches 63% is measured.

[0097] Then, in a step S609, the inertia is sought. Now, the calculation of the inertia will be described.

[0098] The transmission function of the motor can be equivalent to a primary delay system model, and gain G is represented by the following equation (1):

G=K/(1+sT)  (1)

[0099] Where, K=1/Ke, and Ke is reverse start constant. Further,

T=RJ/(Kt×Ke)  (2)

[0100] Where, R is coil resistance of the motor, J is load inertia and K is torque constant of the motor.

[0101] Further, the response property of the motor is represented by the following equation (3) on the basis of the above equation (1):

h(t)=K/(1−et/T)  (3)

[0102] From the equation (3), when t=T, h(t)∝0.632×K.

[0103] Namely, by seeking the time when the speed reaches 63.2% after the motor was started, from J=(Ke×Kt×t)/R (alteration from the above equation (2)), J can be sought, since R, Kt and Ke of the motor are already known.

[0104] Then, in a step S610, the servo constant is calculated. In this calculation, 0 dB intersecting point of the open loop property of the motor is sought by ω=1/T from the above equations (1) and (2) by using the previously sought inertia J, and, an inflection point of the PI filter is set with respect to the intersecting point, and the PI filter constant (proportion item constant and integration item constant shown in FIG. 4) is sought.

[0105] Then, in a step S611, the servo constant setting flag is cleared, and the servo constant setting sequence is finished. In a step S612, it is judged whether the motor has already been driven. If not driven, in a step S613, initial setting of resistors, timers and ports is effected, and, in a step S614, the motor is driven. On the other hand, if the motor has already been driven, the program is jumped.

[0106] Then, in a step S615, it is judged whether there is CAP1 interruption. If there is the interruption, in a step S616, the motor speed is calculated. This interruption is generated whenever the rising edge of the pulse is reached from the MR sensor. On the other hand, if there is no interruption, the program is bypassed.

[0107] Then, in a step S617, it is judged whether there is the servo constant setting control flag. If no under servo constant setting control, in a step S618, it is judged whether there is servo-control loop interruption. If there is control interruption, in a step S619, the difference between the target speed and the actual speed is calculated, and, in a step S620, PI filter calculation is effected by using the previously sought constant, and, in a step S621, the PWM width is set.

[0108] On the other hand, in the step S617, if under the servo constant setting control, in a step S618, the program bypasses the steps S619 to S621 (PWM width calculating sequence). Further, in the step S618, if there is no servo-control interruption, the PWM width calculating sequence is bypassed.

[0109] Then, in a step S622, it is judged whether there is PWM interruption. If there is interruption, in a step S623, the pulses are outputted to the port; whereas, if there is no interruption, the pulses are not outputted. The PWM interruption is generated at carrier frequency pre-set. For example, when the carrier frequency is 20 kHz, interruption of 20 kHz is generated.

[0110] Whenever this interruption is generated, if the PWM pulse having the width sought by calculation is outputted, the PWM pulse having carrier of 20 kHz can be formed.

[0111] In this way, according to the illustrated embodiment, there is provided a leaning sequence in which the motor servo constant setting period is given by the control CPU of the image forming apparatus in the time period other than the image forming period, and, in this period, the DSP calculates the load inertia of the motor, and the servo constant is sought on the basis of the inertia. With this arrangement, for example, even in a system in which the load inertia is greatly changed in accordance with the difference in toner capacity of the toner cartridge or the difference in kind of the cartridge, the proper servo constant can be used, with the result that the control is stabilized and good image quality can be obtained.

[0112]FIGS. 7A and 7B are views showing a DC brushless motor of inner rotor type used in the present invention and a brushless motor of outer rotor type. In FIG. 7A, a DC brushless motor of outer rotor type comprises a rotor 701, stators 702 and windings or coils 703. On the other hand, in FIG. 7B, a DC brushless motor of inner rotor type comprises a rotor 704, stators 705 and windings or coils 706. As can be seen from the drawings, the motor of inner rotor type has smaller rotor which leads to small inertia.

[0113] Namely, since the inertia is small, mechanical response of the motor becomes fast accordingly, with the result that frequency of the servo-control loop in the servo-control block diagram of FIG. 4 can be hastened. That is to say, in a system having relatively great load fluctuation frequency, by hastening the frequency of the servo-control loop, fluctuation suppressing effect due to servo can be enhanced.

[0114] In this way, in the illustrated embodiment, by using the above-mentioned motor servo-control and by using the DC brushless motor of inner rotor type having small inertia, the present invention is effective in a system in which rotational fluctuation of the motor due to load fluctuation is generated at relatively high frequency.

[0115]FIG. 8 shows a first alteration of the internal circuitry of the motor unit shown in FIG. 3. In this alteration, the servo constant is determined in accordance with the kind of the motor. The same elements as those in the embodiment shown in FIG. 3 are designated by the same reference numerals and explanation thereof will be omitted.

[0116] In FIG. 8, the reference numerals 533, 534 indicate discrimination signals of motor unit. In this alteration, discrimination signal lines (discrimination signals 533, 534 for the motor) is provided in association with the servo-control apparatus. The DSP 501 determines the servo constant on the basis of the motor discrimination signals 533, 534.

[0117] For example, when it is assumed that the outer rotor motor is designated if the motor discrimination signals 533, 534 are “0”, “1”, respectively, and the inner rotor motor is designated if the motor discrimination signals 533, 534 are “1”, “1”, respectively, the DSP 501 selects the corresponding servo constant from servo constant table previously stored for the respective motors and effects the servo-control. By discriminating the motor type on the basis of the motor discrimination signals 533, 534 and by selecting and using the optimum servo constant for the motor, stable motor servo-control can be realized.

[0118] Next, the motor servo-control effected by the DSP 501 will be explained.

[0119]FIG. 9 is a flow chart showing a servo-control routine of the DSP 501 shown in FIG. 8.

[0120] First of all, in a step 401, it is judged whether the servo constant is set. If No, in a step 402, the motor type is discriminated. This discrimination is effected by using the motor discrimination signals 533, 534 shown in FIG. 8.

[0121] Then, in a step 403, the servo constant corresponding to the result of the discrimination signals is derived from the lookup table. The lookup table is previously stored in a memory (not shown) of the DSP. Further, the servo constant indicates constants of the proportion item and integration item of the PI filter and a constant of gain.

[0122] Then, in a step 404, the derived servo constant is set in a calculation formula.

[0123] On the other hand, in the step 404, after the servo constant was set once, when the servo-control routine is carried out again, in the step 401, it is judged that the servo constant has already been set, and the routine is jumped to a step 405.

[0124] Then, in steps 405 to 407, it is judged whether the motor is started or stopped.

[0125] In a control task (not shown), when a motor start flag or a motor stop flag is set and the servo-control routine is carried out, in the step 405, the flag is checked. If it is judged that the motor should be started in the step 405, the motor drive signal 529 is made active, and, in the step 407, the predetermined PWM value is given, thereby accelerating the motor. On the other hand, if it is judged that the motor should be stopped in the step 405, in the step 406, the motor drive signal 529 is made disable to make the PWM signal zero, thereby stopping the motor.

[0126] Then, in a step 408, it is judged whether there is interruption of capture. The capture circuit (not shown) is designed so that, whenever the rising edge of the pulse of the MR sensor signal 331 shown in FIG. 8 is reached, such capture interruption is generated.

[0127] In the step 408, if there is the interruption of capture, in a step 409, interval between the interruptions is measured to derive the number of revolutions of the motor. For example, when it is assumed that 300 MR sensor pulses are generated per one revolution and the pulse interval is t (s), the rotational speed of the motor becomes (2π/300÷t) rad/s. On the other hand, in the step 408, if there is no capture interruption, the motor speed is not calculated.

[0128] Then, in a step 410, it is judged whether there is control interruption. It is designed so that, when the servo-control loop effects the control with 1 kHz, interruption of 1 kHz is generated. If the interruption is generated, in a step 411, the pre-set target speed with the actual speed detected by the capture, and a result is PI-calculated in a step 412. The proportion item constant, integration item constant and gain constant set in the step 404 are calculated, and a result is PWM-calculated in a step 413, thereby deriving the PWM width. As a result, the desired PWM widths are outputted at an interval of 1 kHz. Namely, the servo-control loop having control frequency of 1 kHz can be realized.

[0129] Then, in a step 414, it is judged whether there is PWM interruption.

[0130] This interruption is generated every 20 kHz by a pre-designed PWM circuit (not shown).

[0131] In the step 414, if the PWM interruption is detected, in a step 415, the pulses having PWM width previously sought in the step 413 are outputted. On the other hand, if the PWM interruption is not detected, the PWM output is not effected. In this way, the PWM pulse having carrier frequency of 20 kHz can be outputted.

[0132] As mentioned above, in the first alteration, the motor type is discriminated by the type discrimination signals provided in each motor unit, and, on the basis of this, the servo constant corresponding to the motor type is derived from the table, and the servo-control is performed by sing this servo constant.

[0133] In this way, the present invention can be realized with a simple construction.

[0134] Next, a circuit operation of this motor servo-control circuit will be explained. First of all, when the motor drive command is emitted from the CPU through the serial communication line 532, the pre-driver 503 ascertains the position of the rotor detected by the hole sensors 525 to 527 and determines the switching timing to obtain the desired rotation and effect control so as to obtain the desired rotational direction and to flow the desired electric current into the motor coil.

[0135] Namely, the switching control of the N-chMOS transistors 515 to 520 is effected to obtain the desired rotational direction, and the N-chMOS transistors 515, 517, 519 are PWM-switched to flow the desired current into the coil. In this case, the gate voltages for the N-chMOS transistors 515, 517, 519 are increased to Vcc+10V by the charge pump circuit 507.

[0136] For example, when the pre-driver 503 ascertains the position of the rotor of the motor on the basis of the hole sensor signals amplified by the hole sensor amplifiers 511 to 513 and the hole sensors 525 to 527 and switches the electric current direction from the U-phase 522 to the W-phase 523 to obtain the desired rotational direction, the pre-driver 503 turns ON the N-chMOS transistors 515, 518 and turns OFF the N-chMOS transistors 516, 517, 519, 520. As a result, the electric current path extends from Vcc to the electric current detecting resistor 521 through the transistor 515, U-phase output 522, V-phase output 523 and transistor 518, thereby generating a magnetic force in the predetermined coil. In this case, the PWM signal 530 given by the DSP 501 is combined with the switching signals, and the N-chMOS transistors 515 is PWM-controlled by the pre-driver 503.

[0137] Accordingly, the ON-duty electric current defined by the PWM signal flows from the U-phase to the V-phase. In this way, the exciting switching control for switching the electric current to the U-phase, V-phase and W-phase is effected so that the motor is rotated in the predetermined direction, thereby generating torque by relative electromagnetic action between the main pole magnet (not shown) and the coil.

[0138] When the motor is subjected to the exciting switching control to rotate the rotor in this way, the pre-set MR sensor magnetized pattern is detected by the MR sensor 528, and 360 pulses per one revolution are outputted. Namely, the signal having frequency corresponding to the revolution number of the motor is obtained, and this signal is sent to the DSP 501 through the amplifier 514 and the MR sensor signal 531.

[0139] The DSP 501 measures the pulse interval between the pulses from the MR sensor signal line 531 and seeks the speed (rad/s) of the motor and compares the motor speed with the target control speed (set target speed which can be altered) and performs PI filter calculation (not shown) and gain addition calculation (not shown) to derive the PWM pulse width and sends the pulse width to the pre-driver 503 as the PWm signal 530 to control the current to be supplied to the motor, thereby controlling the motor to rotate at the target speed.

[0140] In this way, the DSP 501 generates the PWM signal and effects the switching of the output stage N-chMOS transistor by combining the PWM signal with the switching signals, thereby performing the servo-control to rotate the motor at the desired number of revolutions. On the other hand, the position of the main pole is detected by the hole sensors 525 to 527, and the pre-driver 503 performs the switching control by using the hole sensor signals to rotate the rotor in the desired rotational direction. Further, the pre-driver 503 detects the current flowing through the motor by the electric current detecting resistor 521, and, there is provided protecting means for limiting the electric current by the current limiter circuit 510 if the current greater than a predetermined value flows.

[0141]FIG. 10 shows a second alteration of the internal circuitry of the motor unit shown in FIG. 3. The same elements as those in the embodiment shown in FIG. 3 are designated by the same reference numerals and explanation thereof will b omitted.

[0142] The second alteration shown in FIG. 10 differs from the first alteration shown in FIG. 8 in the point that, in place of the motor discrimination signals 533, 534, a memory 535 is provided in a motor unit 502, and the DSP 501 and the motor unit 502 effect communication through serial communication.

[0143] An operation will be explained with reference to FIG. 11.

[0144]FIG. 11 is a flow chart of the servo-control of the DSP 501 shown in FIG. 10.

[0145] First of all, in a step 601, it is judged whether the servo constant is set. If No, in a step 602, the serial communication to the motor unit is effected to read-in the contents of the memory of the motor unit, thereby recognizing control information of the motor unit.

[0146] Then, in a step 603, the information recognized in the previous step, i.e., servo constant is set.

[0147] On the other hand, in the step 603, after the servo constant was set once, when the servo-control routine is carried out again, in the step 601, it is judged that the servo constant has already been set, and the routine is jumped to a step 604.

[0148] Then, in steps 604 to 606, it is judged whether the motor is started or stopped.

[0149] In a control takes (not shown), when a motor start flag or a motor step flag is set and the servo-control routine is carried out, in the step 604, the flag is checked. If it is judged that the motor should be started in the step 604, in a step 605, the motor drive command is sent to the motor unit by serial communication, and the predetermined PWM value is given, thereby accelerating the motor.

[0150] On the other hand, if it is judged that the motor should be stopped in the step 604, in the step 606, the motor stop command is sent to the motor unit by serial communication, the PWM value is made zero, thereby stopping the motor.

[0151] Since steps 607 to 614 are the same as the sets 408 to 415 in FIG. 4, explanation thereof will be omitted.

[0152] In this way, in the second alteration, the communication between the DSP and the motor unit is effected by serial communication, and the memory means is provided in the motor unit, and the motor control parameters are previously stored in the memory means.

[0153] The DSP reads-in the servo constant of the motor through the serial communication, and the servo-control is effected on the basis of the servo constant.

[0154] Accordingly, the lookup table memory in the motor unit of the first alteration can be omitted, and many control parameter information can b stored in the motor unit, thereby further improving the servo-control accuracy.

[0155] In the present invention, while an example that the six motors are used was explained, the number of motors is not limited to plural, but, the present invention can be applied to a single motor.

[0156] As mentioned above, according to the present invention, the motor servo-control apparatus which can cope with the change in speed of the motor quickly and stably can be obtained.

[0157] In the motor servo-control apparatus according to the present invention, since the DSP effecting quick product/addition calculation by obtaining the PWM signal by inputting the rotational speed signal from the MR sensor to the DSP, the apparatus is suitable for servo-control, and, since control conditions can be programmed in accordance with load conditions (torque, inertia, gain and the like), the control has flexibility.

[0158] By combining the PWM signal from the DSP with the directly inputted switching signal in the pre-driver, the number of signal lines (number of pins) can be reduced. Further, by controlling the plurality of motors, the number of signal lines can be reduced.

[0159] By controlling the servo-control of the plural motors collectively by the single DSP, the total cost of the system can be reduced, and the system control of the plural motors can easily be performed.

[0160] Further, by using the motor servo-control apparatus having the above-mentioned construction in the image forming apparatus, in an image forming apparatus including a plurality of servo motors, by effecting the servo-control by using means for determining the servo constant of the motors in accordance with the load conditions for the driving of the servo motors and means for measuring the load inertia in the time period other than the image forming period and for calculating the servo constants on the basis of measured results, even in a system in which load inertia and torque are greatly differentiated, since the optimum servo constants are always set, the stable motor servo-control can be achieved, thereby obtaining the good image quality.

[0161] Further, by providing means for effecting control without interference between the plural servo-control loops, the plurality of motors can be servo-controlled independently by the single processor, thereby reducing the system cost.

[0162] Further, by using the DC brushless motor of inner rotor type having small inertia as the driving motor to hasten the servo-control loop, even in the load in which period of rotation fluctuation due to load fluctuation is relatively high, the stable servo-control can be effected.

[0163] According to the present invention, means for discriminating the servo motor type are provided, and the servo constant is determined by this means, and the motor is servo-controlled on the basis of the servo constant. Alternatively, the servo motor is provided with the memory means in which the servo constant is stored, and, by effecting the servo-control on the basis of read-out servo constant, even in an apparatus in which a plurality kinds of motors are used, the respective motors can always be servo-controlled with optimum servo constants.

[0164] Particularly, as is in an image forming apparatus, in a system in which motors manufactured by plural manufacturers are used in the same driving area, by discriminating the motor type or by directly getting the servo constant information optimum to the motor and by effecting the servo-control on the basis of the motor type or servo constant information, not only stability of the motor servo-control is enhanced but also the motors having different property and manufactured by plural manufactures can be used similarly without changing control program and arrangement of the image forming apparatus, thereby improving productivity and motor supplying stability. 

What is claimed is:
 1. A servo-control apparatus for a motor, comprising: rotational speed signal generating means for generating a rotational speed signal corresponding to a rotational speed of a motor; digital control means for generating a PWM signal for determining an exciting electric current to be supplied to a coil of said motor in accordance with the rotational speed signal from said rotational speed signal generating means; position detecting means for detecting a rotational position of said motor and for generating a position detection signal corresponding to a detected position; a pre-driver for forming a switching signal for switching the exciting electric current to be supplied to said coil of said motor in accordance with the position detection signal from said position detecting means and for combining the switching signal with the PWM signal from said digital control means to generate an electric current control signal; and a driver for driving said motor on the basis of the electric current control signal from said pre-driver.
 2. A servo-control apparatus according to claim 1, wherein said digital control means have therein target speed setting means for setting a target speed which can be altered and generate the PWM signal in accordance with the target speed from said target speed setting means and the rotational speed signal from said rotational speed signal generating means.
 3. A servo-control apparatus according to claim 1, wherein said pre-driver has a logic circuit for combining the switching signal with the PWM signal, and a control circuit for boosting an output signal from said logic circuit to output it as the electric current control signal.
 4. A servo-control apparatus according to claim 1, wherein said digital control means are a DSP.
 5. A servo-control apparatus for servo-controlling a plurality of motors, comprising: a plurality of rotational speed signal generating means for generating rotational speed signals corresponding to rotational speeds of said plurality of motors, respectively; digital control means for generating PWM signals for determining exciting electric currents to be supplied to coils of said plurality of motors in accordance with the rotational speed signals from said plurality of rotational speed signal generating means, respectively; a plurality of position detecting means for detecting rotor positions of said plurality of motors, respectively; a plurality of pre-drivers for forming switching signals for switching the exciting electric currents to be supplied to said coils of said plurality of motors in accordance with rotor position detection results from said plurality of rotor position detecting means and for combining the switching signals with the PWM signals from said digital control means to generate electric current control signals, respectively; and a plurality of drivers for driving said plurality of motors on the basis of the electric current control signals from said pre-drivers.
 6. A servo-control apparatus according to claim 5, wherein the motor servo-control apparatus is used in an image forming apparatus.
 7. A servo-control apparatus for a motor, comprising: rotational speed signal generating means for generating a rotational speed signal corresponding to a rotational speed of a motor; digital control means for generating a PWM signal for determining an exciting electric current to be supplied to a coil of said motor in accordance with the rotational speed signal from said rotational speed signal generating means; position detecting means for detecting a rotational position of said motor and for generating a position detection signal corresponding to a detected position; switching signal generating means for generating a switching signal for switching the exciting electric current to be supplied to said coil of said motor in accordance with the position detection signal from said position detecting means; and a driver for driving said motor on the basis of the switching signal from said switching signal generating means and the PWM signal from said digital control means.
 8. A servo-control apparatus for a motor, comprising: rotational speed signal generating means for generating rotational speed signals corresponding to rotational speeds of a plurality of motors; and digital control means for determining exciting electric currents to be supplied to coils of said plurality of motors in accordance with the rotational speed signals from said rotational speed signal generating means; and wherein said digital control means comprise target speed setting means for setting target speeds, rotational speed calculating means for obtaining the rotational speeds from said rotational speed signal generating means, and servo calculation means for adding servo constants to differences between the target speeds from said target speed setting means and the rotational speeds from said rotational speed calculating means, servo-control means for determining the electric currents to be supplied to said coils of said motors on the basis of results of said servo calculation means are provided in association with said respective motors, and there are provided timing control means for controlling control timings of said servo-control means for said respective motors.
 9. A servo-control apparatus according to claim 8, wherein said digital control means comprise servo constant setting judging means for judging whether a servo constant is set, and servo constant setting means for setting the servo constant when it is judged that the servo constant should be set by said servo constant setting judging means.
 10. A servo-control apparatus according to claim 8, wherein said timing control means comprise target speed selecting means for selecting target speeds for said motors, means for selecting the servo constants and said servo calculation means for said motors, rotational speed calculating means for obtaining the rotational speeds from said rotational speed signal generating means, and means for selecting speed information from the rotational speed signals for said motors, and further wherein the selection is effected in a time-lapse fashion for said motors.
 11. A servo-control apparatus according to claim 9, wherein said servo constant selecting means measure a time period until said motor reaches a predetermined speed and calculate the servo constant from a measured result.
 12. A servo-control apparatus according to claim 8, wherein each of said motors is a motor of inner rotor type having a stator coil for generating a magnetic field in an excited condition, and a rotor magnet for obtaining a rotational force under relative electromagnetic action with an electric current magnetic field within said stator coil.
 13. A servo-control apparatus for a motor, comprising: recognizing means for recognizing a kind of a motor; rotational speed signal generating means for generating a rotational speed signal corresponding to a rotational speed of said motor; and digital control means for generating a PWM signal for determining an exciting electric current to be supplied to a coil of said motor in accordance with the rotational speed signal from said rotational speed signal generating means; and wherein said digital control means comprise target speed setting means for setting a target speed, rotational speed calculating means for obtaining the rotational speed from said rotational speed signal generating means, and servo calculation means for adding a servo constant in accordance with a difference between the target speed from said target speed setting means and the rotational speed from said rotational speed calculating means and a recognition result from said recognizing means, thereby generating the PWM signal to be supplied to said coil of said motor in accordance with a calculation result of said servo calculation means.
 14. A servo-control apparatus according to claim 13, wherein said recognizing means recognize a torque constant and inertia of said servo motor.
 15. A servo-control apparatus according to claim 13, wherein said recognizing means have recognizing signal generating means corresponding to the kind of the motor and determine the servo constant of said servo calculation means of said digital control means in accordance with a recognizing signal from said recognizing signal generating means.
 16. A servo-control apparatus according to claim 13, wherein said recognizing means have a memory storing a recognizing signal corresponding to the kind of the motor and determine the servo constant of said servo calculation means of said digital control means in accordance with the recognizing signal from said memory.
 17. A servo-control apparatus according to claim 13, wherein there are provided a plurality of said motors and a plurality of said rotational speed signal generating means, and said digital control means generate the PWM signals for determining the exciting electric currents to be supplied to said coils of said plurality of motors, respectively and servo-control said plurality of motors collectively.
 18. A servo-control apparatus for a motor, comprising: recognizing means for recognizing a kind of a motor; rotational speed signal generating means for generating a rotational speed signal corresponding to a rotational speed of said motor; and digital control means for generating a PWM signal for determining an exciting electric current to be supplied to a coil of said motor in accordance with the rotational speed signal from and rotational speed signal generating means, said digital control means comprising target speed setting means for setting a target speed, rotational speed calculating means for obtaining the rotational speed from said rotational speed signal generating means, and servo calculation means for adding a servo constant in accordance with a difference between the target speed from said target speed setting means and the rotational speed from said rotational speed calculating means and a recognition result from said recognizing means, thereby generating the PWM signal to be supplied to said coil of said motor in accordance with a calculation result of said servo calculation means; position detecting means for detecting a rotational position of said motor and for generating a position detection signal corresponding to a detected position; a pre-driver for forming a switching signal for switching the exciting electric current to be supplied to said coil of said motor in accordance with the position detection signal from said position detecting means and for overlapping the PWM signal from said digital control means with the switching signal; and a driver for driving said motor on the basis of the switching signal overlapped by the PWM signal from said pre-driver.
 19. A servo-control apparatus for switching exciting electric currents to be supplied to coils of a motor in accordance with a rotor position detection result of said motor and for controlling the exciting electric currents to be supplied to said coils of said motor on the basis of a rotational speed signal corresponding to a rotational speed of said motor, comprising: recognizing means for recognizing a kind of said motor; digital control means for determining a servo constant in accordance with a recognition result of said recognizing means and for generating a PWM signal for determining the exciting electric current to be supplied to said coil of said motor in accordance with the servo constant and the rotational speed signal; switching signal generating means for generating switching signals for switching the exciting electric currents to be supplied to said coils of said motor in accordance with the rotor position detection result; and a driver for driving said motor on the basis of the switching signal from said switching signal generating means and the PWM signal froms aid digital control means. 